Acuity of Sound Localisation: A Topography of Auditory Space. III. Monaural Hearing Conditions

Abstract

A study is reported in which the acuity of azimuth and elevation discrimination under monaural listening conditions was measured. Six subjects localised a sound source (white noise through a speaker) which varied in position over a range of elevations (-40 degrees to +40 degrees) and azimuths (0 degrees to 180 degrees), at 10 degrees intervals, on the left side of the head. Monaural listening conditions were established by the fitting of an ear defender and one earmuff to the right ear. The absolute and algebraic, azimuth and elevation errors were measured for all subjects at each position of the source. The results indicate that all subjects suffered a marked reduction of azimuth acuity under monaural conditions, although a coarse capacity to discriminate azimuth still remained. Considerable between-subject variability was observed. Front/back discrimination was retained, although it was slightly impaired compared to that observed under normal listening conditions. Elevation discrimination was, on the whole, quite good under monaural conditions. However, a comparison of the performance of these subjects under monaural conditions with that observed under normal listening conditions indicated that some reduction in elevation localisation acuity occurred in the frontal quadrants in the median plane and in the upper quadrants of more lateral source positions. The reduction in acuity seen in these regions is attributed to the loss of information from the pinna of the occluded ear rather than to the observed reduction in azimuth error. The results provide partial support for the binaural pinna disparity model.

Directional sensitivity of sound-pressure levels in the human ear canal

“…For example, spectral cues to sound location have been invoked to account for the accuracy of localization by monaural listeners (Harris and Sergeant, 1971; Butler and Flannery, 1980; Musicant and Butler, 1984;Oldfield and Parker, 1986). Moreover, distortions of the shape of the external ear, which modify its transfer function, result in substantial deterioration in sound localization accuracy Oldfield and Parker, 1984;Humanski and Butler, 1988).…”

Binaural hearing ability with mastoid applied bilateral bone conduction stimulation in normal hearing subjects

“…In a recent study, patients with severe acquired unilateral conductive hearing loss showed improved horizontal localization ability when rehabilitated with BCHA (Agterberg et al, 2011). We note that such results do not prove the use of binaural information, as monaural information can be used to some extent for localization tasks (Oldfield and Parker, 1986). The Agterberg et al study did not include any additional binaural test as, for example, spatial release from masking.…”

Auditory Spatial Perception: Auditory Localization

“…The relative importance of the interaural spectral cues to the localization of sound sources at different elevations is hard to generalize since it varies with the lateral position of the sound source (e.g., Jin et al, 2004). Oldfield and Parker (1986) demonstrated that monaural localization in the vertical plane, which does not take advantage of the interaural spectral cues, is 15 relatively good but somewhat less accurate than binaural localization. Similar data were reported by Humanski and Butler (1988) and Slattery and Middlebrooks (1994).…”